Optimization of photocatalytic degradation of rhodamine B using Box–Behnken experimental design: Mineralization and mechanism

Abstract

The aim of this work was to optimize the photocatalytic degradation of rhodamine B (RhB) using a four-factor Box-Behnken experimental design, and the study was carried out under artificial irradiation (24-W UV lamp) using ZnO in suspension. The Box-Behnken model has been validated with an error less than 5%. A total (100%) RhB removal and COD abatement rates were reached under optimal conditions of treatment time, ZnO dose, and stirring speed at different concentrations of dye. The study of the effect of irradiation type (solar and UV lamp) on the degradation of RhB showed that solar irradiation gave a better rate of degradation with complete discoloration after 2 hr. The study of RhB degradation mechanism indicates that O •− 2 were the main active species for the degradation of this pollutant. The comparison between the degradation of RhB alone and RhB prepared with varnish (as it is usually used in industry) revealed that degradation of RhB alone is faster comparing than that of RhB/varnish mixture. The results showed that the biodegradability was improved after a contact time of 60 min with a BOD 5 /COD ratio increasing from 0.23 to 0.90. © 2020 Water Environment Federation • Practitioner points • Optimization of the photocatalytic degradation of rhodamine B using a four-factor Box-Behnken experimental design. • Investigation of dye mineralization. • The degradation mechanism of rhodamine. • Biodegradability assessment based on the BOD 5 /COD ratio.

Photocatalytic treatment of Crystal Violet in aqueous solution:Box–Behnkenoptimization and degradation mechanism

“…These results (Figure 6) show that the use of a solar source gave higher yields (up to 96%) than photocatalysis by UV lamp (62%) after 120 min of irradiation. Similar results were also observed by Tassalit et al for tartrazine degradation, 13 and by Madjene et al for Rhodamine degradation 27 …”

“…Scavengers which are specifically trapping active species have been used to assess the photocatalytic reaction mechanism of the pollutant studied since they can modify the kinetic profile of the reaction, providing information on the participation of different active species. Tert‐butanol, ammonium oxalate and the benzoquinone were used to show the role of hydroxyl radicals (OH • ), holes ( t + ) and superoxide anion (O 2 •− ) in the oxidation mechanism 27 …”

“…A commercial ZnO was used with 99% purity, whose characteristics were published elsewhere 27 . All the reagents were obtained on the market with quality grade.…”

Sulfur-doped carbon dots synthesis under microwave irradiation as turn-off fluorescent sensor for Cr(III)

“…S3c demonstrated a decrease in PL intensity after 60 min and 120 min of exposure by 14% and 21%, respectively. In traditional fluorescent dyes such as Rhodamine 6G, the reduction in PL intensity after 120 min of continuous exposure was almost 54% (Madjene et al 2021). This shows that the S-CDs were more resistant to photobleaching.…”